The present invention relates broadly to trench digging machines. More specifically, the present invention relates to a heavy rock trencher with a unique position-variable boom system which mechanically compensates during operation by changing the operative center of gravity.
It will be appreciated that a large number of trencher systems exist in the prior art. Typical prior art trenchers may comprise some type of tow vehicle such as a motorized cab or tractor for propulsion, but more often they comprise a single integrated motorized unit. An associated digger boom and shovel apparatus adapted to extend outwardly and downwardly from the cab operatively digs a trench at a selective depth and angle. Such booms typically comprise elongated, articulated members terminating in an enlarged shovel, or a continuous track of scoops or scrapers.
Typical of such prior art trenchers known to me are the diggers disclosed by Hovland, U.S. Pat. No. 915,963 issued Mar. 23, 1909; McIninch, U.S. Pat. No. 2,748,504, issued June 5, 1956; by Burns et al., U.S. Pat. No. 2,783,556, issued Mar. 5, 1957; and, by Ruatti in U.S. Pat. No. 1,769,074, issued July 1, 1930.
A wide variety of mechanical arrangements have been proposed to control an inclinable digger boom, including U.S. Pat. No. 1,239,474 issued Sep. 11, 1917 to French. The French '474 reference discloses the basic concept of employing an inclined ramp which is driven by an entrained chain for digging teeth. Through various mechanical linkages shown in the prior art known to me, such a chain digging assembly can be moved upwardly or downwardly, to the left or the right, or toward or away from the tractor or truck upon which it is mounted. For example, the Ruatti '074 device, although rather complex, demonstrates the broad concept of providing a variable-incline working ramp for establishing the trench incline in which the pivot point is variable with respect to the cab on which it is mounted. Petraud, U.S. Pat. No. 4,535,555, issued Aug. 20, 1985, illustrates the use of a hydraulic cylinder adapted to rotatably adjust the inclination of cooperating guide cutters. Additionally, a number of complex laser-signal systems also have been introduced to assist the operator to define the desired angle of inclination. As will be appreciated by those skilled in the operation of trenching equipment, many of the problems previously encountered with the use of early trenching devices thus have been successfully addressed in the prior art.
As a rule of thumb, successful rock trenching generally requires weight and power. One major disadvantage encountered with the operation of known conventional trenching equipment is that the tractor can easily overcenter or tilt when the boom is raised out of the ground. And, when the boom is forced downwardly, a deleterious change in the center of gravity and unwanted tilting moments can result as well. The latter problem is aggravated when the operator forces the boom against rock to be cut, creating pivoting between the boom load point and the counterweights. Typically front-mounted counterweights are employed to neutralize weight moments to prevent unwanted tilting. But such weights then interfere when the boom is forced into the ground to dig, since the then-required downward force is at least partially neutralized by the counterweights. It is well known that without regard to the size or weight of the load, the cab will overcenter and may topple if the trencher boom is forced downwardly too hard.
The heavy weight (i.e. 100 tons with counterweights included) known "fixed pivot point" equipment further aggravates stability problems. When heavier digging booms are fitted to conventional systems, more counterweights must then be added as well. None of the trenching systems known to me provides an adequate system for compensating for changes in the center of gravity of the trencher boom, without adding or removing counterweights. Moreover, no convenient method has been devised in the prior art to facilitate use of heavier or longer booms to enhance digging power where the soil is particular hard or rocky. Even when the soil is not particularly hard or rocky, multiple counterweights can interfere with mobility and operation capacity. The required counterweights also contribute to a not-insignificant transportation problem for the contractor, whose over-the-road trucking equipment must haul the machine and all the counterweights. Besides the weight problem, the apparatus must be dissembled before hauling, and then reassembled at the construction site.
Other means of preventing over-center problems include rather complex metering systems or warning devices. However, such devices typically do not improve operation of the trencher, but merely assist the operator to avoid exceeding the extension limits of the boom to prevent accidental toppling. Of course, the efficacy of such devices depends mainly upon the operator's level of skill, understanding, and attention to its operation.
Some attempts to solve the problem have been discussed in the prior art. As shown by Ealy, Pat. No. 4,255,883, issued on Mar. 17, 1981, an hydraulic cylinder may be used to move the control boom upwardly to vary the position both vertically and horizontally of the center of gravity. However, the aforementioned systems are generally overly complex and have proven ineffective in operation.
Hence it would seem desirable to provide more effective boom control means which automatically compensate for a change in the center of gravity of the trencher boom without the necessity of varying counterweights, whereby to permit the use of longer, heavier booms and to facilitate extension or contraction of the boom.
Finally, it is desirable to provide a trencher which can be easily broken down for relocation to another site. Generally, the boom must be removed and tractored separately from the tractor and trailer combination. As will be appreciated, breaking down typical prior art trenchers is very difficult and requires a great deal of additional time, resulting in additional expense to the operators. A boom system which could be quickly and conveniently broken down for transport would thus prove most advantageous and cost-effective.